Inkjet Printing for Advanced Packaging

As advanced packaging evolves to meet the demands of artificial intelligence (AI)-driven systems, it continues to push the boundaries in terms of heterogeneous integration, package size and cost-efficiency. This development brings conventional coating methods such as spin and spray coating to their physical and economic limits. In contrast, inkjet printing emerges as an additive technology for semiconductor manufacturing, offering distinct advantages over traditional deposition methods, particularly in terms of material efficiency, scalability and its ability to pattern surfaces without the need for subsequent exposure and development. 

Within the presentation we will show recent advancements in inkjet printing of photoresists, dielectrics and bonding materials, such as laser release and temporary bonding layers. These materials are essential for the creation of three-dimensional integrated circuits (3D ICs), passivation or interconnect structures in fan-out wafer-level packaging (FOWLP) and system-in-package (SiP) platforms. Especially for the high data transfer rates, low latencies and enhanced power requirements inherent to AI applications, a significantly higher level of integration between logic, memory and power supply components must be achieved compared to traditional computer architectures. The SiP approach leads to an evolution towards ever larger packages that integrate the diverse chips and range over multiple exposure fields of a stepper. This decreases the area utilization efficiency on 300 mm wafers and starts a trend towards rectangular panels with sizes up to 700 mm x 700 mm. The large and rectangular substrates as well as warpage and topographical irregularities caused by varying chip heights pose ever greater challenges for the classical spin coating process. The flexible chuck design and scalable print head assembly of an inkjet printer, however, makes inkjet printing a promising technology for the coating of non-standard-sized substrates. For feature sizes up to 50 µm, direct patterning can be applied, which circumvents the need for lithography and allows for the printing of multiple materials within the same print head assembly, additionally accelerating the process. Smaller feature sizes can be created by combining the inkjet printing of photoresist with photolithography. Due to the full utilization of the deposited photoresist and the possibility to spare out certain areas, a decrease in material usage of up to 80 % compared to spin coating can be achieved, which minimizes waste and reduces process costs.

The possibility for selective ink deposition not only reduces the number of necessary process steps but also allows for the dynamic adaptation of the printed image. In SiPs, for example, the die positions are influenced by the pick-and-place and molding processes, which leads to significant wafer-to-wafer variation. Due to its digital deposition approach inkjet printing allows for the integration of inline metrology systems with a dynamic feedback loop. Die positions and substrate topography can be measured in real time, which allows for an initial defect detection as well as the creation of custom print images that avoid damaged areas and adjust for die placement and wafer warpage. The inline metrology system can furthermore be used for quality control after the print by recording high-resolution film thickness data and optical images. Integrating metrology data directly into the printing workflow can thus increase yield and reduce process variability. 

These innovations position inkjet printing as a flexible, scalable and cost-effective technology for next-generation packaging. By combining digital deposition, a flexible system design and real-time process control, inkjet printing addresses the limitations of classical coating methods and supports the continued miniaturization and integration demands of AI and high-performance computing platforms.